Clinical trial of experimental HIV vaccine halted

Experts from the National Institute of Allergy and Infectious Diseases (MD, USA), part of the National Institutes of Health, have made the decision to stop administering doses of an experimental HIV vaccine, due to results released by an independent data and safety monitoring board (DSMB).

The Phase IIb/III clinical trial, called HVTN 702 or Uhambo, is being conducted in South Africa and was testing a prime-boost vaccine regimen. The vaccine regimen being administered was an adapted version of a previous regimen used in the RV144 clinical trial in Thailand.

The vaccine regimen used previously in Thailand is the only ever regimen found to show protection against HIV. The Uhambo vaccine regimen, adapted to tackle the HIV subtype Clade C, was thought to be promising. However, during an interim review, the DSMB found that the vaccine offers a poor level of protection.

The Uhambo study involved 5407 men and women aged 18–35, spread over 14 sites. The participants were HIV-negative and were given either a placebo or the vaccine regimen over 18 months. They were also offered other HIV prevention methods such as oral pre-exposure prophylaxis.

The DSMB looked at how many participants were diagnosed with HIV after 60% had been in the study for over 18 months. The analysis revealed that 129 in the vaccine group and 123 in placebo group had HIV infections.

Based on these results the DSMB decided that the vaccine regimen was ineffective. Although more HIV infections were seen in the vaccine group, this difference was not significant and there was no evidence that the vaccine either increased or decreased the likelihood of HIV infection. In addition, the DSMB found no safety concerns.

Glenda Gray, HVTN 702 Protocol Chair commented: “The people of South Africa have made history by answering this important scientific question. Sadly, we wish the answer was different.”

“We commend all the sites, the South African communities and each participant for their tireless commitment to finding solutions to the HIV epidemic,” added Protocol Co-Chair Linda-Gail Bekker.

Despite this disappointment, the National Institutes of Health are currently exploring other avenues for HIV prevention, such as late-stage vaccine trials, Imbokodo and Mosaico, which are testing a novel mosaic vaccine regimen. Tests on broadly neutralizing antibodies are also under way. In addition, other long-acting methods are being studied, including long-acting injectable antiretroviral drugs, implants and vaginal rings.

Investigation of a wide range of prevention strategies is vital, especially in countries such as South Africa, which has one of the highest HIV rates in the world. Although these recent results are not ideal, the development of other promising HIV prevention tools continues.